Cell Membranes & Movement Across Them 2006-2007
Cell (plasma) membrane Cells need an inside & an outside separate cell from its environment cell membrane is the boundary IN food - s - proteins - s salts O 2 H 2 O OUT waste - ammonia - salts - CO 2 - H 2 O products - proteins cell needs materials in & products or waste out
Building a membrane How do you build a barrier that keeps the watery contents of the cell separate from the watery environment? What substance do you know that doesn t mix with water? FATS LIPIDS Remember: oil & water don t mix!!
Lipids of cell membrane Membrane is made of special kind of lipid phospholipids split personality Membrane is a double layer phospholipid bilayer inside cell attracted to water phosphate lipid outside cell repelled by water
Semi-permeable membrane Cell membrane controls what gets in or out Need to allow some materials but not all to pass through the membrane semi-permeable only some material can get in or out So what needs to get across the membrane? lipids aa O 2 H 2 O salt waste
Crossing the cell membrane What molecules can get through the cell membrane directly? s and oils can pass directly through inside cell waste lipid salt outside cell aa H 2 O but what about other stuff?
Cell membrane channels Need to make doors through membrane protein channels allow substances in & out specific channels allow specific material in & out H 2 O channel, salt channel, channel, etc. inside cell H 2 O aa waste salt outside cell
How do you build a semi-permeable cell membrane? Channels are made of proteins proteins both like water & like lipids bi-lipid membrane protein channels in bi-lipid membrane
Protein channels Proteins act as doors in the membrane channels to move specific molecules through cell membrane HIGH LOW
Movement through the channel Why do molecules move through membrane if you give them a channel?? HIGH? LOW
Molecules move from high to low Diffusion move from HIGH to LOW concentration
Diffusion Move from HIGH to LOW concentration passive transport no energy needed diffusion of water diffusion osmosis
Simple Diffusion Move from HIGH to LOW inside cell LOW Which way will move? HIGH outside cell
Facilitated Diffusion Move from HIGH to LOW through a channel inside cell LOW Which way will move? HIGH outside cell
Diffusion Move from HIGH to LOW concentration directly through membrane simple diffusion no energy needed help through a protein channel facilitated diffusion (with help) no energy needed HIGH LOW
Simple vs. facilitated diffusion simple diffusion facilitated diffusion inside cell lipid inside cell H 2 O protein channel outside cell outside cell H 2 O
Active transport Cells may need molecules to move against concentration hill need to pump uphill from LOW to HIGH using energy protein pump requires energy ATP ATP
Transport summary simple diffusion facilitated diffusion active transport ATP
Osmosis Movement of Water Across Cell Membrane 2006-2007
Osmosis Water is very important, so we talk about water separately Osmosis diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane
Keeping water balance Cell survival depends on balancing water uptake & water loss freshwater balanced saltwater
1 Keeping right amount of water in cell Freshwater a cell in fresh water high concentration of water around cell cell gains water example: Paramecium problem: cells gain water, swell & can burst water continually enters Paramecium cell solution: contractile vacuole pumps water out of cell KABOOM! No problem, here freshwater
Controlling water Contractile vacuole in Paramecium
2 Keeping right amount of water in cell Saltwater a cell in salt water low concentration of water around cell cell loses water example: shellfish problem: cell loses water in plants: plasmolysis in animals: shrinking cell solution: take up water I m shrinking, I m shrinking! I will survive! saltwater
3 Keeping right amount of water in cell Balanced conditions no difference in concentration of water between cell & environment cell in equilibrium example: blood problem: none water flows across membrane equally, in both directions volume of cell doesn t change That s better! I could be better balanced